All trains must have a track to run on. Therefore; it is very important that when you build a model train track layout that you use the right track for the right job. If you are modeling in the steam era, you will need a turn table or a Y track to turn your locomotive around. Diesel Electric locomotive can run in any direction. When it comes to the radius of the curves is all comes down to the gauge you are modeling.
When modeling in N gauge track, the main line curves should have at least a radius of 11.25″. The larger the radius the better the locomotives will negotiate the turns, especially at full speed. If the curves are too tight the locomotive could bind or even derail.
Now let”s look at HO scale train track. If you are modeling in steam all 4-8-4 engines need at least a 22″ radius. Also the 2-8-4 and 2-10-4″s need at least 22″ radius. The 2-8-0s, 2-6-2s, 0-6-0s, and 4-4-0s locomotives must have a minimum radius of 18″. Most of the diesel electric locomotives in HO gauge must have at least a radius of 18″, except for the EMD DDX40AX must have at least a 22″ radius. Also, most switchers in HO gauge can negotiate a 15″ radius curve.
The O gauge tracks are not measured by radius, but by diameter. For example, 0-27 means the track has a 27″ diameter. Most O gauge street cars can handle an 0-27 curve. The PA-1, E7, General Electric Dash 9, Fairbands-Moses, U33C, FP45, SD45, SD90, and General Electric Amtrak locomotive all need an O-31 diameter curve. Whereas, the FA-1, F7, F3, Baldwin Shark, GP9, General Electric Dash 9, GP38, Bl2, NW-2, General Electric 44 Ton, locomotives all need an O-27 diameter curve. Now let”s look at the steam locomotive track diameter curves. The 4-8-4,2-8-4 locomotive can negotiate a O-31 diameter curve. Whereas, the 4-6-4 locomotive really needs an O-42 curve diameter track to negotiate the curve without any problem.
The G gauge or Large Scale trains need at least a 4″ diameter curve. Theses radius are the minimum for the locomotive that is operating on that track. Even though, this is the recommended minimum curve, you can always model your train track in a larger radius that will make the trains look even more realistic. Also, just because the locomotive can negotiate the curves you have to take into consideration that some long passenger cars may need a larger radius than the locomotive. Remember to make your track look realistic you must ballast the track and install culverts and ditches so that the water can be carried away from the rails. You also need to make sure that you have great electrical connection on your entire track to keep your trains running smoothly as they should. As always remember the main thing is to always have fun when it comes to building your model train layout.